The present invention relates to a display panel, a control display panel and an insert molding method for integrally molding an insert material such as sheet.
Recently, from home electric appliances such as microwave ovens and rice cookers to information equipment such as mobile phones, in the display section of an electronic apparatus, a display panel in which film and resin material are integrally molded is widely used. Some panels are mounted with the switching function section, which is called a membrane switch (sheet switch).
In order to simplify the operation procedures of an electronic apparatus, it is desired that the display panel have a simple configuration. However, accompanying the multifunction tendency in electronic apparatuses, the simpler configuration leads to a more complicated operation. Contrarily, to simplify the operation, when various switches such as a menu key and setting key are disposed in the display panel, a disadvantage that the configuration of the display panel itself becomes complicated results in a high cost. Therefore, in order to employ a display panel with a simple configuration and to simplify the operation thereof, a configuration in which the display area of the display panel, which has a double-layered structure, has been employed to improve the display efficiency within the limited display/operation area.
To form the display area of the display panel into a double-layered structure, a method, in which a printed layer (foil) is formed in an in-molding manner on the front and rear surfaces of a panel base body such as transparent resin having translucency, is available. Thus, by forming the display area of the display panel into a double-layered structure, the density of the information to be displayed is increased and a user-friendly display panel can be obtained.
As a method for integrally molding the printed sheet simultaneously, there is known a method of insert molding, in which a printed sheet printed on the front surface before-hand is placed in dies, and then, a resin material is injected into the dies and pressed; thereby the printed sheet and the resin material are integrally molded (for example, JP-A-6-209849). The insert molding as described above includes a front insertion method, in which the printed sheet is disposed on the front side surface of the molding article, and a rear insertion method, in which a printed sheet is disposed on the rear surface side of a molding article which has translucency.
However, in a process in which the above-mentioned front printed sheet and the rear printed sheet are adhered to the panel base body of a transparent resin or the like using an adhesive, a double-sided adhesive tape or the like, the adhered face between the rear printed sheet and the panel base body is seen from the front side resulting in an undesirable state in appearance. Also, the display panel is illuminated by a light source such as an LED from the rear face side, occasionally, uneven display and/or incorrect display due to leaked light are seen from the front side surface of the display panel. This is caused by the fact that, if there is any gap between the rear printed sheet and panel base body, the light readily leaks therefrom. To prevent uneven display or incorrect display, the both sides of the above are required to be adhered reliably with no gap; and when adhering them, uneven adhesion and inclusion of dust are required to be prevented
As a method for integrating the panel base body and the printed sheet with a high tightness of contact, an insert molding is available. However, when the above described display panel is molded employing the insert molding, a problem is caused in any one of the front insertion method and the rear insertion method.
FIG. 36A shows a switch section of a display panel, which is molded by the front insertion method. FIG. 36B is a schematic sectional view showing the display section of the same display panel. In the front insertion method, the light from a light source 4 at the illuminated (ON state) side is transmitted through a translucent portion 3a of a printed sheet 3A placed over the front side surface of the display panel 1A. However, because the thickness of the panel base body 6 reaches to the light path length up to the translucent portion 3a, a part of the light from the light source 4 reaches to the neighboring translucent portion 3b, Since the translucent portion 3b allows the light from the light source 5 at the un-illuminated side (OFF state) in FIG. 36B to transmit therethrough, a leaked light is caused. That is, the translucent portion 3a, which should not be illuminated, is illuminated. As a result, the light from the neighboring light source is mixed and displayed resulting in an unsatisfactory visibility as the display panel.
On the other hand, FIG. 37A shows a switch section of a display panel molded by the rear insertion method. FIG. 37B is a schematic sectional view showing the display section of the same display panel. In the rear insertion method, a printed sheet 3B is disposed on the rear surface of the display panel 1B. Accordingly, since the printed portion is positioned close to the light source, light leakage is eliminated. Thus, even when the light sources are positioned close to each other, the light can be displayed with no mixture of light. However, on the other hand, when the switch press member 8 is repeatedly depressed to turn the switch 7 ON/OFF, since the depression direction coincides with the direction peeling off the printed sheet 3B from the panel base body 6, the peeling-off of the printed sheet 3B is accelerated.
Further, when the display panel 1B is viewed from the direction “V” in FIG. 37B, since the panel base body 3 is transparent, an engagement unit (including rib, catch, screw hole etc.) 9 for attaching the display panel 1 to the electronic apparatus are seen resulting in a problem in appearance.
Therefore, a display panel in which the printed sheet has a double-layered structure, has been proposed. That is, on the front side surface of the configuration formed by the above-described front insertion method, still another layer; i.e., a transparent material 10 applied with printed sheet 3D over the front surface thereof is overlapped. FIGS. 38A and 38B show examples of the display panel of the double-layered structure. Owing to this configuration, retaining units 9 are concealed by the printed area of the printed sheet 3C; thus the problem in appearance can be eliminated. It is arranged so that the switch operation is made via the printed sheet 3D of the outermost layer; thus the peel-off problem also can be eliminated. However, to join the transparent material 10 to the printed sheet 3D and to join the panel base body 6 to the printed sheet 3C, a total two times of the injection molding process are required. Further, another step to join the molded pieces to each other is required leading to a complicated manufacturing process. Furthermore, the performance of the ink or the like are required to withstand high temperatures for a long period of time. Therefore, this method is hardly put to practical use. Further, in this method also, as shown in FIG. 36B, same as the front insertion method, due to the thickness of the panel base body 6, the problem of light leakage is not eliminated.
Further, as an example of related insert molding methods, there is known an insert molding method in which an adapter secures a resin path (refer to, for example, JP-B-5-065329 (2-3 pages and FIG. 1)).
In an insert molding method disclosed in JP-B-5-065329, a sprue communicating with a cavity is disposed in the central area of the lower die, and on the periphery of the sprue, an adapter is inserted communicating with the cavity so as to come out and retreat. The sprue is supported on a first eject plate, and communicates with a screw extrusion molding machine. The adapter projects above a second eject plate placed on the first eject plate and is supported via a pin. The adapter is located at the cavity side and is equipped with a flange, which is fitted into an annular groove formed in the periphery portion of the sprue. The second eject plate is equipped with a return pin, which penetrates through the lower die, and by engaging with the upper die, the second eject plate is made to retreat, and when the adapter is lowered, the flange is engaged with the inside of the annular groove.
In the insert molding method according to JP-B-5-065329, the adapter secures the resin path and an insert material is also fixed to the adapter. Therefore, the resin supplied to the inside of the cavity flows between the insert materials, and by the injection pressure or the press pressure including the injection pressure, both insert materials are molded into a configuration of the dies. At the same time, the materials are integrated being sandwiched therebetween; thus the molding is completed.
However, the insert molding method according to JP-B-5-065329 has the following problems. That is, although both of the front and rear surfaces of the molded article is covered with the insert material, in a state of the molded article, in which the resin material and the insert material are integrally molded, the insert material is occasionally peeled off; or during molding, the resin material occasionally flows between the die and the insert material. Due to the force of flowing resin material, the insert material is occasionally warped within the molding dies; thus, the desired configuration is hardly molded stably.